1. Field of the Invention
The present invention relates to a recording liquid particularly suited to ink-jet recording systems in which recording is performed by ejecting ink droplets from a minute ejection opening (or ejection orifice) provided in a recording head, and an ink-jet process that employs it.
2. Related Background Art
Hitherto known as inks used in writing utensils such as felt pens and fountain pens are those comprising a dye or pigment which serves as a coloring material, dissolved or dispersed in water, and an organic solvent or a mixture of these which serves as a medium. It is also known to add surface active agents, humectants, mildewproofing agents, viscosity modifiers, pH adjusters, etc. therein.
The inks as mentioned above are known to be used also in ink-jet recording systems in which recording is performed by forming and flying ink droplets from an ejection orifice by using mechanical energy, electrostatic energy or heat energy, and adhering on a recording medium.
Preferable performances of ink-jet recording liquids include the following:
(1) The recording liquids can be stably stored for a long period of time, and do not cause clogging; PA0 (2) they have liquid properties such as viscosity, surface tension, and conductivity fitted to ejection conditions such as shapes of the orifice, materials, and drive frequencies; PA0 (3) they may not form any deposits around the cross section of the ink flow path or ejection orifice and may not change the flying course of droplets; PA0 (4) they may not attack surrounding materials; PA0 (5) they may not be irritative to human bodies; PA0 (6) they have an excellent safety against smell, toxicity and flammability; PA0 (7) they can be readily fixed to the recording medium and can give rich smoothness and less feathering to the peripheries of dots; PA0 (8) they can give a sharp printed image; and PA0 (9) they can give a printed image having excellent water resistance and light-resistance.
In particular, in the system in which the droplets are formed by using heat energy, a matter of importance is the phenomenon that deposits are formed around the cross section of the ink flow path or ejection orifice in the course of the ejection of ink. Once the deposits are formed on a heat energy source or in the vicinity thereof, it may occur that they suppress the heat energy from being effectively transmitted, make unstable the generation of bubbles which are the source of ejection force, or divert the flying course from the desired course. As a result, it may follow that prints cannot be obtained with sharpness, or, in an extreme instance, droplets can not be ejected. This is the reason why there is a demand for recording liquids that may not form any deposits in the vicinity of the heat energy source.
Commonly available ink-jet recording liquids are mainly composed of a water-soluble dye as a coloring material, water, a water-soluble organic solvent (such as diethylene glycol and polyethylene glycol), and contain besides these a small amount of organic or inorganic impurities. Various proposals to decrease the deposits have been made on such recording liquids from the respective standpoints.
For example, U.S. Pat. No. 4,396,429 discloses a recording liquid in which the content of m-phenylenediamine in ink has been controlled to not more than 1,000 ppm, and U.S. Pat. No. 4,435,717 discloses a recording liquid containing a dye having no amino group.
Such recording liquids, however, certainly do not form any deposits on thermally affected surfaces when used shortly after they have been prepared, but apparently form deposits when used after they have been stored for a long period of time, bringing about difficulty in ejection.